Processing for high permeability silicon steel comprising copper

ABSTRACT

A process for producing silicon steel having a cube-on-edge orientation and a permeability of at least 1850 (G/Oe) at 10 oersteds, which includes the steps of: cold rolling silicon steel; annealing the cold rolled steel prior to a final cold roll, at a temperature of from 1400* to 1700*F for a period of from 15 seconds to 2 hours; cooling the annealed steel at a rate substantially equivalent to a still air cool; and cold rolling the cooled steel at a reduction of at least 80 percent.

United States Patent [1 1 1 3,855,021 Salsgiver et al. v Dec. 17, 1974 PROCESSING FOR HIGH PERMEABILITY OTHER PUBLICATIONS SILICON STEEL COMPRISING COPPER [75] Inventors: James A. Salsgiver, Sarver; Frank A.

Malagari, Freeport, both of Pa. [73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa. [22] Filed: May 7, 1973 [21] Appl. No.: 358,238

[52] US. Cl. 148/112, 75/123 L, 148/31.55, 148/1 1 1 [51] Int. Cl. l-IOlt' 1/04 [58] Field of Search 148/112, 111, 110, 31.55; 75/123 L [56] References Cited UNITED STATES PATENTS 3,159,511 12/1964 Taguchi et a1. 148/1 11 3,287,184 11/1966 Koh 148/113 3,345,219 10/1967 Detert 148/112 3,632,456 1/1972 Sakakura et al. 148/111 3,671,337 6/1972 Kurnai et a1. 148/112 Lyman, T., Metals Handbook, ASM, Cleveland, 1948, p. 628, (TA472 A3).

Kussmann, A., et al., Gekupferter Stahl For Transform, in Stahl and Eisen, 50, (1930), pp. 1 194-1 197, (T8300 87) Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Vincent G. Giola; Robert F. Dropkin 5 7 ABSTRACT A process for producing silicon steel having a cubeon-edge orientation and a permeability of at least 1850 (G/O,,) at 10 oersteds, which includes the steps of: cold rolling silicon steel; annealing the cold rolled steel prior to a final cold roll, at a temperature of from 1400 to 1700F for a period of from 15 seconds to 2 hours; cooling the annealed steel at a rate substantially equivalent to a still air cool; and cold rolling the cooled steel at a reduction of at least 80 percent.

12 Claims, No Drawings PROCESSING FOR HIGH PERMEABILITY SILICON STEEL COMPRISING COPPER The present invention relates to a process for producing electromagnetic silicon steel having a cube-on-edge orientation and a permeability of at least 1850 (G/O at 10 oersteds.

Oriented silicon steels containing 2.60 to 4.0 percent silicon are generally produced by processes which involve hot rolling, a double cold reduction, an anneal before each cold roll and a high temperature texture anneal. Characterizing these steels are permeabilities at 10 oersteds of from 1790 to 1840 (6/0 In recent years a number of patents have disclosed silicon steels with permeabilities in excess of 1850 (6/0,) at 10 oersteds. Of these, US. Pat. Nos. 3,287,183, 3,632,456 and 3,636,579 appear to be the most interesting from a processing standpoint. US. Pat. No. 3,287,183 which issued on Nov. 22, 1966 reveals that a steel composed of specific amounts of carbon, silicon, aluminum, sulfur and iron could be processed into a high permeability silicon steel by cold rolling from 5 to 40 percent, annealing at a temperature of from l742 to 2192F so as to precipitate AlN, cold rolling from 81 to 95 percent, decarburizing and final texture annealing. More recently, similar processing for similar alloys was disclosed in US. Pat. Nos. 3,632,456 and 3,636,579, which respectively issued on Jan. 4, 1972 and Jan. 25, 1972. Each of these patents refer to cooling rates following the anneal in which MN is precipitated. US. Pat. No. 3,632,456 anneals a hot rolled band at a temperature of from 1382 to 2192F depending upon its silicon content, rapidly cools the annealed band and then proceeds to subject it to at least two cold rollings. U.S. Pat. No. 3,636,579 anneals steel containing 2.5 to 4.0 percent silicon at a temperature of from l742 to 2192F, quenches it from said temperature to a temperature at least as low as 752 F and then cold rolls it.

Described herein is another, and improved method for producing silicon steel having a cube-on-edge orientation and a permeability of at least 1850 (6/0 at 10 oersteds from steel of a particular chemistry. The method includes the steps of: cold rolling silicon steel; annealing the cold rolled steel prior to a final cold roll, at a temperature of from 1400 to 1700F for a periiod of from seconds to 2 hours; cooling the annealed steel at a rate substantially equivalent to a still air cool; and cold rolling the cooled steel at a reduction of at least 80 percent. It differs and is contradictory to the methods of heretofore referred to U.S. Pat. Nos. 3,287,183, 3,632,456 and 3,636,579 in that: US. Pat. No. 3,287,183 discloses a minimum annealing temperature of 1742F and not a maximum annealing temperature of 1700F; US. Pat. No. 3,632,456 calls for a hot rolled band anneal at a temperature in excess of 1742F for steels containing at least 2.5 Si and a rapid cool therefrom; and US. Pat. No. 3,636,579 discloses a minimum annealing temperature of 1742F for steels containing at least 2.5% Si and a rapid cool from said annealing temperature. Moreover, the chemistry of the steel being processed in accordance with the present invention differs from that being processed in said heretofore referred to patents.

It is accordingly an object of the present invention to provide a process for producing electromagnetic silicon steel having a cube-on-edge orientation and a permeability of at least 1850 (6/0.) at 10 oersteds.

The present invention provides a method for producing silicon steel having a cube-on-edge orientation and a permeability of at least 1850 (G/O and preferably at least 1900 (G/O at 10 oersteds. Involved therein are the steps of: preparing a melt of silicon steel having, by weight, up to 0.07% carbon, from 2.60 to 4.0% silicon, from 0.03 to 0.24% manganese, from 0.01 to 0.07% sulfur, from 0.015 to 0.04% aluminum, up to 0.02% nitrogen, and from 0.1 to 0.5% copper; casting the steel; hot rolling the steel into a hot rolled band, cold rolling the hot rolled band with or without an intermediate anneal between the hot rolling and the cold rolling, the intermediate anneal being at a maximum temperature of 1700F; subjecting the steel to at least one additional cold rolling; subjecting the steel to a final annealing prior to the final cold rolling; decarburizing the steel; and final texture annealing the steel. Also included, and significantly so, are the specific steps of: carrying out the final anneal prior to the final cold rolling at a temperature of from l400 to 1700F for a period of from 15 seconds to 2 hours; cooling the annealed steel at a rate substantially equivalent to a still air cool; and cold rolling the cooled steel at a reduction of at least percent. Preferred conditions include annealing at a temperature of from 1450 to 1650F and cold rolling at a reduction of at least percent. For purposes of definition, still air cools include those wherein the steel is cooled in a static atmosphere as well as those wherein there is relative motion between the atmosphere and the steel, as in a continuous processing line, so long as there is no deliverate intention to cause the motion for cooling purposes. Moreover, for purposes of definition, all gaseous atmospheres are considered to have the same cooling effect as air. Hence, all open cools are at a rate substantially equivalent to a still air cool unless a liquid quenching medium or forced gaseous atmosphere is employed, and a forced gaseous atmosphere is one in which motion is .deliverately imparted to the atmosphere for cooling purposes.

Melting, casting, hot rolling, annealing, cold rolling, decarburizing and final texture annealing'do not involve any novel procedures, as far as techniques are concerned, and with regard to them, the invention encompasses all applicable steel making procedures. Annealing at a temperature of from l400 to 1700F for the final anneal prior to the final cold roll is, however, believed to be particularly beneficial in that it conditions the steel for cold rolling, provides an operation during which inhibitors can form, and most importantly, increases the uniformity in which the inhibitors are distributed as essentially only ferrite phase is present in the steel at temperatures below 1700F, contrasted to the presence of austenite and ferrite phases and different solubilities for the inhibiting elements in each phase at somewhat higher temperatures. By inhibitors, the invention primarily pertains to aluminum nitride, and manganese sulfide and/or manganese copper sulfide, which are discussed in greater detail hereinbelow. No criticality is placed upon the particular annealing atmosphere. Illustrative atmospheres therefore include nitrogen; reducing gases such as hydrogen; inert gases such as argon; air; and mixtures thereof. For similar reasons, as with the final anneal prior to the final cold roll the hot rolled band should not be annealed at temperatures in excess of 1700F; and when a hot rolled band anneal is desired it is preferred to carry it out at a temperature of from 1400 to 1700F. The annealed hot rolled band is generally cooled at a rate substantially equivalent to a still air cool. As to the cold rolling, it should be pointed out that several roll passes can constitute a single cold rolling operation, and that plural cold rolling operations exist only when cold rolling passes are separated by. an anneal.

The steel melt must include a silicon, aluminum, manganese, sulfur and copper. Silicon is necessary as it increases the steels resistivity, decreases it magnetostriction, decreases its magnetocrystalline anisotropy and hence decreases its core loss. Aluminum, manganese and sulfur are necessary as they form inhibitors which are essential to controlling the steels orientation and its properties which are dependent thereon. More specifically, aluminum combines with nitrogen, in the steel or from the atmosphere, to form aluminum nitride, and manganese combines with sulfur to form manganese sulfide and/or manganese copper sulfide; and these compounds act so as to inhibit normal grain growth during the final texture anneal, while at the same time, aiding in the development of secondary recrystallized grains having the desired cube-on-edge orientation. Copper in addition to possibly forming manganese copper sulfide, is believed to be beneficial in that it is hypothesized that copper can lower the annealing temperature, improve rollability, simplify melting and relax annealing atmosphere requirements.

A steel in which the process of the present invention is particularly adaptable to consists essentially of, by weight, from 0.02 to 0.07% carbon, from 2.60 to 3.5% silicon, a manganese equivalent of from 0.05 to 0.24% as expressed by an equivalency equation of %Mn (0.1 to 0.25) X %Cu, from 0.01 to 0.05% sulfur, from 0.015 to 0.04% aluminum, from 0.0030 to 0.0090% ni trogen, from 0.1 to 0.3% copper, balance iron and residuals; and wherein the ratio of manganese equivalent to sulfur'is in the range of from 2.0 to 4.75. The steel has its chemistry balanced so as to produce a highly beneficial structure when processed according to the present invention.

The following examples are illustrative of several aspects of the invention.

Five samples (Samples 1 of silicon steel were cast and processed into silicon steel having a cube-onedge orientation from 5 different heats of BOF silicon steel. The chemistry of the samples appears hereinbelow in Table l.

4. ture of nitrogen and wet hydrogen, and final annealing for 8 hours in hydrogen at a maximum temperature of 2150F. 7

Samples 1 5 were tested for permeability and core loss. The results of the tests appear hereinbelow in Table II. I

From Table 11, it is clear that the processing of the present invention is highly beneficial to the properties of silicon steel having a cube-on-edge orientation. Samples 1 through 5 were cold rolled, annealed at a temperature of 1475F for 5 minutes, air cooled to room temperature and cold rolled in excess of 80%; and all had permeabilities in excess of 1850 ((3/0 at 10 0,.. Moreover, sample 2 had a permeability in excess of 1900 (GIO It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific examples of the invention described herein.

We claim:

1. In a process for producing electromagnetic silicon steel having a cube-on-edge, orientation and a permeability of at least 1850 6/0 at 10 oersteds, which process includes the steps of: preparing a melt of silicon steel consisting essentially of, by weight, up to 0.07% carbon, from 2.60 to 4.0% silicon, from 0.03 to 0.24% manganese, from 0.01 to 0.07% sulfur, from 0.015 to 0.04% aluminum, up to 0.02% nitrogen, from 0.1 to 0.5% copper and the balance iron; casting said steel; hot rolling said steel into a hot rolled band; cold rolling said hot rolled band with or without an intermediate anneal between said hot rolling and said cold rolling, said intermediate anneal being at a maximum temperature of 1700F; subjecting said band to at least one ad- Processing for the five samples involved soaking at an elevated temperature for several hours, blooming, hot

rolling to a gage of approximately 130 mils, normalizing for 2 minutes at 1650F in air, cold rolling to a gage (if-approximately 92 mils, annealing at 1475F for 5 minutes in impure nitrogen (nitrogen with approximately 0.1 to 10% oxygen), air cooling to room temperature; cold rolling to final gage of approximately 13 mils, decarburizing for 2 minutes at 1475F in a mixditional cold rolling; subjecting said band to a final annealing prior to the final cold rolling; decarburizing said steel, and final texture annealing said steel; the improvement comprising the steps of carrying out said final anneal prior to the final cold rolling at a temperature of from 1400 to 1700F for a period of from 15 seconds to 2 hours; cooling said annealed steel at a rate equivalent to a still air cool, said cool including those wherein the steel is cooled in a static atmosphere or in a continuous processing line where there is some relative motion between the atmosphere and the steel, and excluding furnace cools and those where relative motion is deliberately induced for cooling purposes; and cold rolling said cooled steel at a reduction of at least 80 percent.

2. An improvement according to claim 1, wherein said final anneal prior to the final cold rolling is at a temperature of from l450 to l650F.

3. An improvement according to claim 1, wherein said cooled steel is cold rolled at a reduction of at least 85 percent.

4. An improvement according to claim 1, wherein the hot rolled band is cold rolled without an intermediate anneal between hot rolling and cold rolling.

5. An improvement according to claim 1, wherein the hot rolled band is annealed at a temperature of from l400l700F prior to being cold rolled.

6. An improvement according to claim 5, wherein said annealed hot rolled band is cooled at a rate equivalent to a still air cool prior to being cold rolled.

7. An improvement according to claim 1, wherein said steel consists essentially of, by weight, from 0.02 to 0.07% carbon, from 2.60 to 3.5% silicon, a manganese equivalent of from 0.05 to 0.24%, as expressed by an equivalency equation of %Mn (0.1 to 0.25) X %CU, from 0.01 to 0.05% sulfur, from 0.015 to 0.04% aluminum, from 0.0030 to 0.0090% nitrogen, from 0.1 to 0.3% copper, balance iron and residuals; and wherein the ratio of manganese equivalent to sulfur is in the range of from 2.0 to 4.75.

8. An improvement according to claim 7, wherein said final anneal prior to the final cold rolling is at a temperature of from 1450' to 1650F.

9. An improvement according to claim 7, wherein said cooled steel is cold rolled at a reduction of at least percent.

10. An improvement according to claim 7, wherein the hot rolled band is cold rolled without an intermediate anneal between hot rolling and cold rolling.

11. An improvement according to claim 7, wherein the hot rolled band is annealed at a temperature of from l400 1700F prior to being cold rolled.

12. An improvement according to claim 11, wherein said annealed hot rolled band is cooled at a rate equivalent to a still air cool prior to being cold rolled. 

1. IN A PROCESS FOR PRODUCING ELECTROMAGNETIC SILICON STEEL HAVING A CUBE-ON-EDGE ORIENTATION AND A PERMEABILITY OF AT LEAST 1850 G/OE) AT 10 OERSTEDS, WHICH PROCESS INCLUDES THE STEPS OF: PREPAGING A MELT OF SILICON STEEL CONSISTING ESSENTIALLY OF, BY WEIGHT, UP TO 0.07% CARBON, FROM 2.60 TO 4.0% SILICON, FROM 0.03 TO 0.24% MANGANESE, FROM 0.01 TO 0.07% SULFUR FROM 0.015 TO 0.04% ALUMINUM, UP TO 0.02% NITROGEN, FROM 0.1 TO 0.5% COPPER AND THE BALANCE IRON; CASTING SAID STEEL; HOT ROLLING SAID STEEL INTO A HOT ROLLED BAND; COLD ROLLING SAID HOT ROLLED BAND WITH OR WITHOUT AN INTERMEDIATE ANNEAL BETWEEN SAID HOT ROLLING AND SAID COLD ROLLING, SAID INTERMEDIATE ANNEAL BEING AT A MAXIMUM TEMPERATURE OF 1700*F; SUBJECTING SAID BAND TO AT LEAST ONE ADDITIONAL COLD ROLLING; SUBJECTING SAID BAND TO FINAL ANNEALING PRIOR TO THE FINAL COLD ROLLING; DECARBURIZING SAID STEEL; AND FINAL TEXTURE ANNEALING SAID STEEL FINAL IMPROVEMENT COMPRISING THE STEPS OF CARRYING OUT SAID FINAL ANNEAL PRIOR TO THE FINAL COLD ROLLING AT A TEMPERATURE OF FROM 1400* TO 1700*F FOR A PERIOD OF FROM 15 SECONDS TO 2 HOURS; COOLING SAID ANNEALED STEEL AT A RATE EQUIVALENT TO A STILL AIR COOL, SAID COOL INCLUDING THOSE WHEREIN THE STEEL IS COOLED IN A STATIC ATMOSPHERE OR IN A CONTINUOUS PROCESSING LINE WHERE THERE IS SOME RELATIVE MOTION BETWEEN THE ATMOSPHERE AND THE STEEL, AND EXCLUDING FURNACE COOLS AND THOSE WHERE RELATIVE MOTION IS DELIBERATELY INDUCED FOR COOLING PURPOSES; AND COLD ROLLING SAID COOLED STEEL AT A REDUCTION OF AT LEAST 80 PERCENT.
 2. An improvement according to claim 1, wherein said final anneal prior to the final cold rolling is at a temperature of from 1450* to 1650*F.
 3. An improvement according to claim 1, wherein said cooled steel is cold rolled at a reduction of at least 85 percent.
 4. An improvement according to claim 1, wherein the hot rolled band is cold rolled without an intermediate anneal between hot rolling and cold rolling.
 5. An improvement according to claim 1, wherein the hot rolled band is annealed at a temperature of from 1400*-1700*F prior to being cold rolled.
 6. An improvement according to claim 5, wherein said annealed hot rolled band is cooled at a rate equivalent to a still air cool prior to being cold rolled.
 7. An improvement according to claim 1, wherein said steel consists essentially of, by weight, from 0.02 to 0.07% carbon, from 2.60 to 3.5% silicon, a manganese equivalent of from 0.05 to 0.24%, as expressed by an equivalency equation of %Mn + (0.1 to 0.25) X %CU, from 0.01 to 0.05% sulfur, from 0.015 to 0.04% aluminum, from 0.0030 to 0.0090% nitrogen, from 0.1 to 0.3% copper, balance iron and residuals; and wherein the ratio of manganese equivalent to sulfur is in the range of from 2.0 to 4.75.
 8. An improvement according to claim 7, wherein said final anneal prior to the final cold rolling is at a temperature of from 1450* to 1650*F.
 9. An improvement according to claim 7, wherein said cooled steel is cold rolled at a reduction of at least 85 percent.
 10. An improvement according to claim 7, wherein the hot rolled band is cold rolled without an intermediate anneal between hot rolling and cold rolling.
 11. An improvement according to claim 7, wherein the hot rolled band is annealed at a temperature of from 1400* - 1700*F prior to being cold rolled.
 12. An improvement according to claim 11, wherein said annealed hot rolled band is cooled at a rate equivalent to a still air cool prior to being cold rolled. 